Question

a person need a lens of power -5.5d for correcting his distant vision.For correcting his near vision he need the lens of power +1.5d.What is the focal length of the lens for correcting (1)distant vosion (2)near vision

Answer 1

$\huge\underline\blue{\sf Answer:}$

Focal lenght of distant vision is 18cm and Focal Lenght for near vision is 6 cm

$\huge\underline\blue{\sf Solution:}$

$\large\underline\pink{\sf Given: }$

• Power of lens of distant vision (Concave lens ) =-5.5D

• Power of lens near vision ( Convex lens) =+1.5D

$\large\underline\pink{\sf To\:Find: }$

Focal lenght of lens for (f) :-

• Distant vision (Concave lens ) = ?

• Near vision ( Convex lens ) = ?

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1. Distant Vision :-

We know ,

${\boxed{\sf Power\:of\:lens(P)=\frac{1}{Focal\: Lenght (f)}}}$

$\large\implies{\sf f=\frac{1}{-5.5} }$

$\large\implies{\sf f=0.18m}$

$\large\implies{\sf f=0.18×100}$

$\large\implies{\sf f=18cm}$

$\large\red{\boxed{\sf Focal\: Lenght (f)=18cm}}$

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2. Near Vision :

${\boxed{\sf Power\:of\:lens(P)=\frac{1}{Focal\: Lenght (f)}}}$

$\large\implies{\sf f=\frac{1}{1.5} }$

$\large\implies{\sf f=0.06m }$

$\large\implies{\sf f=0.06×100}$

$\large\implies{\sf f=6cm}$

$\large\red{\boxed{\sf Focal\: Lenght (f)=6cm}}$

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Hence ,

Focal lenght of distant vision is 18cm and Focal Lenght for near vision is 6 cm